Epoxy resins are widely used today in surface coatings, adhesives, castings, laminates, and encapsulation of electronic parts. Most of these epoxy resins are prepared by the reaction of 2,2-bis(4'-hydroxyphenyl)propane [bisphenol A] and epichlorohydrin. This generates a polymer with a backbone composed of ether links between bisphenol A structures and hydroxy propylene moieties. There is also one epoxy group (oxirane) at each end of the polymer backbone. These resins can be cured by reacting their epoxy groups with crosslinking agents, such as anhydrides, amines, and acids. When cured, the epoxides have good tensile strengths, excellent electrical insulating properties, and have outstanding adhesion to many surfaces.
However a major weakness of these conventional epoxy resins is their poor outdoor durability. The ether links in their backbone as well as the aromatic rings lead to poor UV and oxidative stability. Because of this limitation, these epoxy resins cannot be used in systems that require long term outdoor exposure.
Previously two approaches have been taken to make durable epoxides. One involves the synthesis and use of low molecular weight cyclic or acyclic diepoxides and the other involves the synthesis and use of copolymers of glycidyl methacrylate (GMA). Both of these approaches, though they generate epoxides that are more durable than bisphenol A based resins, have significant deficiencies. The cyclic-type of epoxides are not polymers and have only a very low molecular weight segments binding the two epoxy groups. These materials tend not to have the superior physical properties of conventional epoxides. The systems based on random copolymers of GMA do not have the controlled placement of the epoxy groups. That is, these copolymers have the epoxy groups distributed randomly along the entire backbone of the methacrylate chain. The placement of the epoxy groups at the end of the polymer chain, as seen in bisphenol A epoxides, imparts important properties such as toughness. The random placement of the epoxy groups lowers final properties.
The bisphenol A-based epoxides are well known and are items of commerce (e.g., the Epon resins from Shell and the family of DER epoxides from Dow). The cyclic epoxides have also been commercially available (e.g. Union Carbide's ERL-4221, a cycloaliphatic diepoxide).
Methacrylate copolymers that use randomly distributed GMA have been used in the coatings industry (U.S. Pat. Nos. 3,817,946; 4,027,066; 3,730,930; 4,346,144). However, no patents or publications have been identified that report ABA triblock methacrylate polymers with GMA in the A segments.
The patents and publications concerning GTP report the ability to make block structure using that process (U.S. Pat. Nos. 4,417,034; 4,508,880; 4,414,372; 4,524,196; and 4,544,724). However none of these disclose the epoxy triblock structure nor the advantages of that structure as a durable epoxy resin.
Related applications include Ser. Nos. 660,588, now U.S. Pat. No. 4,711,942, and 660,589, now U.S. Pat. No. 4,581,428, filed Oct. 18, 1984; 673,926 filed Nov. 21, 1984, now U.S. Pat. No. 4,681,918; and 676,099 filed Nov. 29, 1984, now abandoned. Also, application Ser. No. 707,193, filed Mar. 1, 1985, now U.S. Pat. No. 4,588,795, which discloses and claims the use of certain types of oxyanion catalyst in group transfer polymerization.
The disclosures of the above-mentioned patents and applications are hereby incorporated by reference.
In the process of the invention, the polymer produced is "living" in that the polymerization is characterized by the presence, in the growing and in the grown polymer, of a moiety containing the aforesaid metal at "living" ends and the activating substituent or diradical, or a tautomer thereof, at "nonliving" ends of the polymer.
Monomers which are useful in group transfer polymerization herein are of the formula CH.sub.2 .dbd.C(Y)X wherein:
X is --CN, --CH.dbd.CHC(O)X' or --C(O)X'; PA1 Y is --H, --CH.sub.3, --CN or --CO.sub.2 R, provided, however, when X is --CH.dbd.CHC(O)X', Y is --H or --CH.sub.3 ; PA1 X' is --OSi(R.sup.1).sub.3, --R, --OR or --NR'R"; each R.sup.1, independently, is H or a hydrocarbyl PA1 radical which is an aliphatic, alicyclic, aromatic or mixed aliphatic-aromatic radical containing up to 20 carbon atoms, provided that at least one R.sup.1 group is not H; PA1 R is a hydrocarbyl radical which is an aliphatic, alicyclic, aromatic or mixed aliphatic-aromatic radical containing up to 20 carbon atoms, or a polymeric radical containing at least 20 carbon atoms, any of said radicals optionally containing one or more ether oxygen atoms within aliphatic segments thereof, optionally containing one or more functional substituents that are unreactive under polymerizing conditions, and optionally containing one or more reactive substituents of the formula --Z'(O)C--C(Y.sup.1)=CH.sub.2 wherein Y.sup.1 is H or CH.sub.3 and Z' is O or NR'; and PA1 each of R' and R" is independently selected from PA1 C.sub.1-4 alkyl. PA1 R.sup.1 is as defined above; PA1 Z is an activating substituent selected from the group PA1 consisting of ##STR1## --SR, --OP(NR'R").sub.2, --OP(OR.sup.1).sub.2, --OP[OSi(R.sup.1).sub.3 ].sub.2 and mixtures thereof wherein R, R.sup.1, R', R", X' and Z' are as defined above; PA1 Z.sup.1 is the activating substituent ##STR2## m is 2, 3 or 4; n is 3, 4 or 5; PA1 M is Si, Sn or Ge, provided, however, when Z is ##STR3## M is Sn or Ge; and each of R.sup.2 and R.sup.3 is independently selected from H and hydrocarbyl, defined as for R above; PA1 (a) at least one of any R, R.sup.2 and R.sup.3 in the initiator optionally containing one or more initiating substituents of the formula --Z.sup.2 --M(R.sup.1).sub.3 wherein PA1 M and R.sup.1 are as defined above; PA1 Z.sup.2 is an activating diradical selected from the group consisting of ##STR4## thereof, wherein R.sup.2, R.sup.3, X', Z', m and n are as defined above provided however when Z.sup.2 is ##STR5## M is Sn or Ge, (b) R.sup.2 and R.sup.3 taken together are ##STR6## if Z is ##STR7## (c) X' and either R.sup.2 or R.sup.3 taken together are ##STR8## if Z is ##STR9## PA1 each end segment being an oxirane-containing acrylic or methacrylic moiety, PA1 said center segment being an acrylic or methacrylic moiety not containing oxirane groups
The initiator used in the polymerization of this invention is a silicon-containing initiator of U.S. Pat. Nos. 4,414,372, 4,524,196, 4,417,034 and 4,508,880 supra, and copending application Ser. Nos. 660,588, 660,589, 673,926 and 676,099. Initiators which are preferred for use herein are of the formula selected from (R.sup.1).sub.3 MZ. (R.sup.1).sub.2 M(Z.sup.1).sub.2 and O[M(R.sup.1).sub.2 X.sup.1 ].sub.2 wherein:
The invention is concerned with ABA triblock polymers that have glycidyl methacrylate (GMA) as the A segments and standard (meth)acrylate monomers as the B segment. These methacrylate triblock polymers have now been synthesized with epoxy groups located only at the ends of the polymer chain. Because their backbone is a (meth)acrylate (meaning acrylate and/or methacrylate) structure, these epoxy resins should be significantly more durable than conventional bisphenol A based epoxides. These new polymers should have better final properties than the cyclic epoxides because the backbone is polymeric in nature. They should be better than conventional GMA polymers that have a random distribution of epoxy groups because all of the epoxy groups are now located at the end of the chains, similar to bisphenol A epoxides.